The present invention relates to an optical module used in optical communication systems, such as a data link and an optical LAN, which utilize light as an information transmitting medium. The invention also relates to a manufacturing method of such an optical module.
The above optical module is classified into two types: a transmitting module having as an optical functional element a light-emitting element such as a semiconductor laser, and a receiving module having as an optical functional element a photodetecting element such as a p-i-n photodiode. For example, U.S. Pat. No. 5,170,453 (corresponding to Japanese Patent Application Unexamined Publication No. Hei. 2-271308) discloses an optical module of this type which enables cost reduction due to a reduced number of parts and the mass-production effect, and which is superior in reliability and durability.
An optical module manufacturing method disclosed in the above patent is summarized below with reference to FIGS. 1 and 2. FIG. 1 shows an assembly of an optical module 1 in a state immediately after resin molding. In this state, an optical connector 2 and lead pins 3 of a lead frame 8 are held by a resin mold member 5. FIG. 2 shows an assembly before being set in metal dies for the resin molding. In FIG. 2, a support member 7 is inserted into a ferule insertion hole 6 to thereby support the optical connector 2 by the lead frame 8. To hold the optical connector 2 more stably, it is further supported by a holding member 9 of the lead frame 8.
As shown in FIG. 2, terminals extending in front of a metal package 10 that is unified with the optical connector 2 and containing an optical functional element are connected by wires 13 to terminals of electronic circuit parts 12 mounted on a circuit board 11 that is placed on the lead frame 8. The lead frame 8 has inner leads 3a and outer leads 3b of the lead pins 3, a mother land (not shown) located inside the inner leads 3a and supporting the circuit board 11, and tie-bars 14 for holding the mother land, lead pins 3, etc.
In the state of FIG. 2, the lead frame 8 and the respective parts are set in metal dies (not shown), and a plasticized resin material is pressure-injected into the metal dies. The resin material is molded as shown in FIG. 1, and the respective parts are held by the resin mold member 5. Finally, the optical module 1 is completed by cutting out unnecessary portions of the lead frame 8.
Compared with the preceding optical module manufacturing method in which respective parts are fixed to a ceramic package with an adhesive, the above method is superior in that it enables cost reduction and mass-production due to rationalization of a manufacturing process. However, although in the above method sufficient studies and improvements have been made of the rationalization of the manufacturing process and the reliability of the molding step using the resin material, no improvements have been made of the grounding of the optical element and the electronic circuits.
In general, in the above optical module, the optical functional element and the electronic circuits are connected to each other by wiring. However, for instance in the case of an optical module in which an optical data link using a laser diode is molded with a resin material, the method of connecting the laser diode and the electronic circuits only by wiring cannot provide sufficient grounding performance, preventing the optical module from exhibiting satisfactory characteristics. Similarly, an optical module having a photodetecting element is susceptible to noises because of insufficient grounding performance.